Human RSV or Respiratory Syncytial Virus is a large RNA virus, member of the family of Paramyxoviridae, subfamily pneumoviridae together with Bovine Respiratory Syncytial Virus. Human RSV is responsible for a spectrum of respiratory tract diseases in people of all ages throughout the world. It is the major cause of lower respiratory tract illness during infancy and childhood. Over half of all infants encounter RSV in their first year of life, and almost all within their first two years. The infection in young children can cause lung damage that persists for years and may contribute to chronic lung disease in later life (chronic wheezing, asthma). Older children and adults often suffer from a (bad) common cold upon RSV infection. In old age, susceptibility again increases, and RSV has been implicated in a number of outbreaks of pneumonia in the aged resulting in significant mortality.
Infection with a virus from a given subgroup does not protect against a subsequent infection with an RSV isolate from the same subgroup in the following winter season. Re-infection with RSV is thus common, despite the existence of only two subtypes, A and B.
Today only three drugs have been approved for use against RSV infection. A first one is ribavirin, a nucleoside analogue that provides an aerosol treatment for serious RSV infection in hospitalized children. The aerosol route of administration, the toxicity (risk of teratogenicity), the cost and the highly variable efficacy limit its use. The other two drugs, RespiGam® (RSV-IG) and Synagis® (palivizumab), polyclonal and monoclonal antibody immunostimulants, are intended to be used in a preventive way. Both are very expensive, and require parenteral administration.
Other attempts to develop a safe and effective RSV vaccine have all met with failure thus far. Inactivated vaccines failed to protect against disease, and in fact in some cases enhanced disease during subsequent infection. Life attenuated vaccines have been tried with limited success. Clearly there is a need for an efficacious non-toxic and easy to administer drug against RSV replication. It would be particularly preferred to provide drugs against RSV replication that could be administered perorally.
A reference on structure-activity relations, in respect of RSV inhibition, of 5-substituted benzimidazole compounds is X. A. Wang et al., Bioorganic and Medicinal Chemistry Letters 17 (2007) 4592-4598.
Compounds that exhibit anti-RSV activity are disclosed in WO2012/080446, WO2012/080447, WO2012/080449, WO2012/080450 and WO2012/080451.
WO-2004/069256 discloses 2-cyanopyrrolopyrimidines and WO-2004/076455 discloses spiro-substituted 2-cyanopyrrolopyrimidines as capthepsin K or S inhibitors useful in the treatment of various pain disorders. Teno N. et al. in Bioorganic & Medicinal Chemistry Letters, vol. 17, 6096-6100 (2007) and Teno N. et al. in J. Med. Chem., vol. 51, 5459-5462 (2008) disclose 2-cyanopyrrolopyrimidines as cathepsin K inhibitors.
Potential problems which RSV antivirals may encounter are toxicity, mutagenicity, lack of selectivity, poor efficacy, poor bioavailability, and difficulty of synthesis.
It is desired to provide new compounds that have antiviral activity. Particularly, it would be desired to provide new drugs that have RSV replication inhibitory activity. Further, it would be desired to retrieve compound structures that allow obtaining antiviral biological activities of the order of magnitude in the stronger regions of the prior art, and preferably at a level of about the most active, more preferably of even stronger activity, than compounds disclosed in the art. A further desire is to find compounds having oral antiviral activity.
There is a need for additional RSV inhibitors that may overcome at least one of these disadvantages or having one of the desired effects.